Emerging Possibilities for Space Propulsion Breakthroughs

Extract from Interstellar Propulsion Society Newsletter, Vol. I, No. I

By Marc G Millis

New ways to think of inertia and gravity
The ideal interstellar drive would have the ability to manipulate the connection between mass and spacetime. One approach is to look for ways to use electromagnetism, a phenomenon for which we are technologically proficient, to control inertial or gravitational forces. It is known that gravity and electromagnetism are coupled phenomena.

In the formalism of general relativity this coupling is described in terms of how mass warps the spacetime against which electromagnetism is measured. In simple terms this has the consequence that gravity appears to bend light, red-shift light and slow time. These observations and the general relativistic formalism that describes them have been confirmed (ref 9, 10). Although gravity's affects on electromagnetism have been confirmed, the possibility of the reverse, of using electromagnetism to affect gravity, is unknown.

Zero Point Energy (ZPE) is the term used to describe the random electromagnetic oscillations that are left in a vacuum after all other energy has been removed (ref 13). This can be explained in terms of quantum theory, where there exists energy even in the absolute lowest state of a harmonic oscillator.

The lowest state of an electromagnetic oscillation is equal to one-half the Planck constant times the frequency. If all the energy for all the possible frequencies is summed up, the result is an enormous energy density, ranging from 1036 to 1070 Joules/m3.

In simplistic terms there is enough energy in a cubic centimeter of the empty vacuum to boil away Earth's oceans.

First predicted in 1948, the ZPE has been linked to a number of experimental observations. Examples include the Casimir effect (ref 14), Van der Waal forces (ref 15), the Lamb-Retherford Shift (ref 10, p. 427), explanations of the Planck blackbody radiation spectrum (ref 16), the stability of the ground state of the hydrogen atom from radiative collapse (ref 17), and the effect of cavities to inhibit or enhance the spontaneous emission from excited atoms (ref 18).

Regarding inertia and gravity theories, they take the perspective that all matter is fundamentally constructed of electrically charged particles and that these particles are constantly interacting with this ZPE background. From this perspective the property of inertia, the resistance to change of a particle's velocity, is described as a high-frequency electromagnetic drag against the Zero Point Fluctuations.

Gravity, the attraction between masses, is described as Van der Waals forces between oscillating dipoles, where these dipoles are the charged particles that have been set into oscillation by the ZPE background.

It should be noted that these theories were not written in the context of propulsion and do not yet provide direct clues for how to electromagnetically manipulate inertia or gravity. Also these theories are still too new to have either been confirmed or discounted. Despite these uncertainties, typical of any fledgling theory, these theories do provide new approaches to the search for breakthrough propulsion physics. Their utility and correctness remains to be determined.

Another viewpoint on gravity and spacetime

The ideal interstellar drive must not use propellant. Instead the ideal drive would have to use some means to push against spacetime itself. One of the major objections to this notion is the issue of conservation of momentum (ref 19).

In order to satisfy conservation of momentum, something must act as a reaction mass. For rockets it is the expelled propellant; for aircraft it is the air. If one considers propelling against spacetime itself, then one must entertain the possibility that the fields of spacetime have an energy or momentum that can serve as a reaction mass.

Although existing physics does not provide this perspective, a recent theory has emerged that might do so. A news article published in December 94 (ref 6) introduced a theory (ref 20) that is challenging Einstein's general theory of relativity. The theory is generating a bit of controversy because it claims that the Einstein field equations need a slight correction.

Without this correction it is claimed that the Einstein equations can only predict the behavior of simple one-body problems (where only one gravitating mass exists whose affect on an inconsequential test particle is described).

For two-body or n-body problems, this new theory shows that the Einstein equations are inadequate. The required correction is that another term must be added to the matter tensor, specifically a term for the stress-energy tensor of the gravitational field itself. This suggests that gravitational fields have an energy and momentum of their own. This may be a foundation to address the issue of a reaction mass for the ideal space drive.

Like the previously mentioned theories, it is uncertain whether this theory is correct or not, but it is certain that this theory adds yet another research path to search for breakthrough propulsion.

But wait, there's more

Another avenue to explore pushing against space is to examine the contents of the vacuum that may be indicative of a reaction mass. In addition to the items mentioned above, consider the following phenomena: Cosmic Background Radiation (ref 21), Virtual Pair Production (ref 22), and Dark Matter (ref 23). Whether any of these may constitute a reaction mass or may be evidence for a reaction mass is uncertain.

In addition to these recent events, there have been occasional surveys by the Air Force and others to examine science that may be applicable to propulsion technology (refs 24-29). The options identified by these studies include assessments of the technological status of many popular ideas, such as light-sails, nuclear rockets, and antimatter rockets, plus they include mention of more speculative work.

Many of the more speculative ideas, from alternative theories of gravity and electromagnetism through unconfirmed anomalous effects, would be relativity simple to test. Very few of these possibilities have been rigorously investigated. As you can see, there are a number of dangling loose ends in physics that may prove to be fruitful paths to the goal of creating the breakthroughs for practical interstellar travel.

Marc G Millis
Space Propulsion Technology Division
NASA Lewis Research Center

References

1. Mallove, E.F., and Matloff, G.L., The Starflight Handbook, Wiley Science Editions, John Wiley and Sons, Inc., New York (1989).
2. Gonick, L., "Science Classics (Warp-and-woof drive)", In Discover, p. 44-54, (DEC 1994).
3. Szpir, M, "Spacetime Hypersurfing?", American Scientist, Vol. 82, p. 422-423, (September-October 1994)
4. Clarke, A. C., "Space Drive: A Fantasy That Could Become Reality", Ad Astra, p. 38, (Nov-Dec 1994)
5. Matthews, R., "Inertia: Does Empty Space Put Up the Resistance?", Science, Vol. 263, p. 612-613, (4 Feb 1994).
6. Peterson, I., "A New Gravity?, Challenging Einstein's General Theory of Relativity", Science News, Vol. 146, p. 376-378, (Dec 3, 1994).
7. Alcubierre, M., "The warp drive: hyper-fast travel within general relativity", In Classical and Quantum Gravity, Vol 11, p. L73- L77, (1994).
8. Bennett, G., "Warp Speed, Fact or Fiction?", Final Frontier, p. 35-39, (September-October 1994).
9. Pool,R., "Closing in On Einstein's Special Theory of Relativity", In Science, Vol. 250, p. 1207-1208, (Nov. 9, 1990).
10. Misner,C.W., Thorne,K.S., and Wheeler,J.A., Gravitation, W.H.Freeman and Co., New York (1973).
11. Haisch, B., Rueda, A., and Puthoff, H.E., "Inertia as a Zero-Point Field Lorentz Force", Physical Review A, Vol. 49, No. 2, p. 678- 694, (FEB 1994)
12. Puthoff,H.E., "Gravity as a zero-point-fluctuation force", Physical Review A, Vol. 39, N. 5, (A89-33278), p. 2333-2342, (Mar 1, 1989).
13. Boyer,T.H., "The Classical Vacuum", Scientific American, p. 70-78, (Aug 1985).
14. Sparnaay, M. J., Measurements of Attractive Forces between Flat Plates, In Physica, Vol. 24, p. 751-764, (1958).
15. Casimir,H.B.G., and Polder, D., "The Influence of Retardation on the London-van der Waals Forces", In Physical Review, Vol.73, N.4, p.360-372, (February 15, 1948).
16. Boyer,T.M., "Random Electrodynamics: The Theory of Classical Electromagnetic Zero-Point Radiation" In Physical Review D, Vol.11, N.4, p.790-808, (Feb 15, 1975).
17. Puthoff,H.E., "Ground State of Hydrogen as a Zero-Point-Fluctuation- Determined State", Physical Review D, Vol.35, No.10, p.3266-3269, (15 May 1987).
18. Haroche,S. and Kleppner,D., "Cavity Quantum Electrodynamics" In Physics Today, p.24-30, (January, 1989).
19. Millis, M. G., "Exploring the Notion of Space Coupling Propulsion", In Vision 21: Space Travel for the Next Millennium, Symposium Proceedings, Apr 1990, NASA-CP-10059, p. 307-316, (1990).
20. Yilmaz, H., "Toward a Field Theory of Gravitation", Il Nuovo Cimento, Vol. 107B, no. 8, p. 941-960, (Aug 1992).
21. Muller, R. A., "The Cosmic Background Radiation and the new Aether Drift", Scientific American, Vol. 238, N. 5, p. 64-74, (May 1978).
22. Kaufmann, W. J. III, Black Holes and Warped Spacetime, pp 206-208, W. H. Freeman and Co., San Francisco, (1979).
23. Krauss, L. M., "Dark Matter in the Universe", Scientific American, p. 58-68, (Dec 1986).
24. Mead, F. B. ,Jr., et al, Advanced Propulsion Concepts – Project Outgrowth, AFRPL-TR-72-31, (JUN 1972).
25. Forward, R. L., "Feasibility of Interstellar Travel: A Review", Acta Astronautica, Vol. 14, p 243-252, (1986)
26. Mead, F. B. ,Jr., "Exotic Concepts for Future Propulsion and Space Travel", Advanced Propulsion Concepts, 1989 JPM Specialist Session, (JANNAF) Chemical Propulsion Information Agency, CPIA Publication 528, p.93-99, (May 24, 1989).
27. Cravens,D.L., Electric Propulsion Study, AL-TR-89-040, Final Report on Contract FO4611-88-C-0014, Air Force Astronautics Lab (AFSC), (Aug 1990).
28. Evans, R.A., British Aerospace Ltd. Co (BAe) University Round Table on Gravitational Research, Report on Meeting held at the NOVOTEL Conf. Ctr., Preston, March 26-27, 1990, FBS 007, (Nov 1990).
29. Forward, R. L., 21st Century Space Propulsion Study, AL-TR-90-030, Final Report on Contract FO4611-87-C-0029, Air Force Astronautics Lab (AFSC), (Oct 1990). – and –Forward,R.L., 21st Century Space Propulsion Study (Addendum), PL-TR-91-3022, Final (Addendum), OLAC Phillips Lab, formally known as Air Force Astronautics Lab (AFSC), (June 1991).